Coated aluminum composition and process



EAHHHHEB United States Patent 3,353,937 Patented Nov. 21, 1967 perature rise and duration of the elevated temperatures. 3,353,937 A particularly advantageous form of aluminum for this COATED ALUMINUM COMPOSITION purpose is cut wire, suitably from about 0.01 to 0.15

AND PROCESS James M. Ford, William M. Minish, and Philip J. Willis,

saltvine, Va. assignors to 01m Mathias Chemical 5 Ordinarily the maximum transverse dimension of suitable Corporation 1 aluminum particles is about 0.25 inch. However, alu- No Drawing Filed June 8 19 Sen 373 505 minum particles of lesser dimensions, for example, filings 9 Claims. (Cl. 44-3) or powder, are not generally contemplated for the production of heat-producing compositions because of the undue This invention rel-ates to a new and improved method 10 violence of their reaction with water. for treating aluminum for use in compositions for the In these mixtures of the prior art, on storage and prior production of heat. The invention is particularly conto use, intimate contact occurs between the aluminum cerned with coating aluminum for use in the manufacture particles and the other components of the drain cleaner of a mixture of dry ingredients capable of reacting rapidly including caustic soda, nitrate of soda, salt and permanto liberate heat when admixed with water. ganates. An undesirable mottled brown or green color Mixtures of chemical agents for this purpose have frequently develops on the aluminum particles. A clean, long been in common use for supplying heat to so-called frosty, white appearance of the aluminum particles in fireless cookers, for the cleaning of grease clogged drains the drain cleaner is considered more desirable. Further, and for other purposes in which the generation of heat is in the preparation of these mixtures, the application of required. A mixture frequently employed for this purpose the other components of the mixture directly with the includes, as its essential heat-producing ingredients, alualuminum is not readily carried out without hazard to minum and an alkaline agent such as sodium hydroxide operators and without clogging of subsequent screens and or potassium hydroxide. The addition of water to the apparatus due to moisture pickup by the caustic which mixture causes the aluminum and alkali to react rapidly, causes the particles to stick together. This invention avoids producing both heat, gas and mechanical agitation. intimate contact between the aluminum particles and Heat-producing mixtures of this type may, and preferthe other components of the drain cleaner mixture and ably do, include, in addition to the principal heat-producavoids aggregating the aluminum particles. The aluminum ing ingreidents, such additional ingredients as may further particles, treated according to the present invention do the desired action, either to increase the production of not discolor on aging in storage in contact with other heat or for other purposes incidental to the use for which components of the mixtures. the mixture is designed. For example, oxidizing agents, The process of the present inuvention consists in applysuch as sodium nitrate, are commonly employed to react ing a substantially uniform, adherent coating of soda ash with the hydrogen released during the principal reaction. to the aluminum particles and then mixing the thus Catalytic agents, additional heat-generating agents, such coated aluminum particles with caustic soda and other as sodium chlorite, and inert ingredients acting merely as components to form novel heat-producing compositions. carriers or fillers, such as sodium chloride, may be em- In one aspect, therefore, the process of the present invenployed. In general, whatever the constitution of the whole tion consists in applying a thin coating of soda ash to the mixture, it is common practice to limit the aluminum conaluminum particles by drying a vigorously agitated mixtent to a range of about 2 percent to about 8 percent by ture of aluminum particles and a strong solution of soda weight of the total composition. The alkaline agent is emash. ployed in an amount at least about twice that required for The operation is most advantageously carried out feedcombination with the aluminum and often constitutes the ing hot soda ash solutions substantially saturated at temmajor ingredient of the composition. peratures of 85 C. to 105 C. The aluminum may be Exemplary compositions may contain: preheated or fed at room temperatures and suflicient heat may be supplied to the reactor to effect the drying. A Percent by welght hot concentrated solution of sodium carbonate is most s" soda 40 to 67 advantageous to reduce dust loss and to build a substansodfum chlonde Oto 25 tial and uniform, frosty white coating on the aluminum sodfum mtrat? 20 to 40 particles. The drying is advantageously carried out in a chlome 10 rotary kiln dryer wherein the mixture is tumbled to pro- Alummum 2 to 8 vide vigorous agitation but any suitable apparatus can be used. The evaporation and drying is carried out in the Total 100 temperature range of 50 to 150 C. and preferably at Minor amounts, usually less than 1 percent, of color- 90 to 110 C. ants, for example, potassium permanganate, stabilizers The ratio of Soda ash PP in the form of COHCEH' and other components may be included. trated solutions to aluminum is suitably from 2 to 6 Heat-producing compositions of the type described Pounds of z s P" 100 of aluminum'ill the form and which are improved by the process of the present of particles. Preferably this ratio is about 4 to 5 pounds of invention are described, for example, in US. Patents Na CO per 100 pounds of aluminum. The concentration 2,371,436; 2,773,040; 2,816,012; and 3,077,455. of soda ash in solution can vary from more dilute to In these mixtures, the aluminum is in divided form saturated concentrations at temperatures up to the boiling and may have variable composition including substanpoint of such solutions. More heat is required in the tially pure aluminum, aluminum alloys and dross or drier using more dilute solutions and less with the more other grossly impure forms of aluminum. Control of concentrated solutions. Advantageously, therefore, the

particle size is important to control the intensity of reaction and heat evolution, particularly the maximum teminch in diameter and from 0.05 to 0.25 inch in length.

soda ash solutions contain a minimum of 20 percent of soda ash and preferably nearer the saturation value of about 45 to 50 grams of Na CO per 100 grams of water, depending on the temperature. For example, a solution saturated at 190 F. (88 C.) containing 31.75% of Na CO and having a specific gravity of approximately 1.296 is suitable. Substantially all of the water thus introduced is removed by evaporation in the drier and the product is obtained as dry, ash-coated, discrete aluminum particles.

While the preceding description is directed to aluminum particles coated with soda ash, which is the preferred embodiment of the invention, other alkali metal salts can be substituted for the soda ash with satisfactory results. Suitable alkali metal salts include potassium carbonate, phosphate and other sodium and potassium salts. Alkaline alkali metal salts which, in 1% aqueous solution, have a pH of about 9 to 12, preferably 11 to 12, are useful. These salts appear to be sufficiently alkaline to etch the aluminum and produce a satisfactory coating. Included among suitable alkali metal salts are:

Sodium carbonate Potassium carbonate Trisodium phosphate Disodium hydrogen phosphate Dipotassium hydrogen phosphate Tripotassium phosphate Tetrasodiurn pyrophosphate Tetrapotassium pyrophosphate Sodium tripolyphosphate Sodium tetraborate.

Mixtures of alkali metal salts are also useful, for example:

Trisodium phosphate (20%) Disodium hydrogen phosphate (80%).

The proportion of alkali metals salts to aluminum varies suitably from 1 to 10 pounds of dissolved salts per 100 pounds of aluminum though for soda ash 2 to 6 pounds per 100 pounds of aluminum is preferred.

Particular advantages of the ash-coated product of this invention include its uniform, clean, frosty white appearance which is not affected by intimate contact with caustic soda or other common components of heat-producing mixtures with which it is combined. The ash-coated particles remain discrete in the manufacturing process and show no tendency to agglomerate in storage under all ordinary conditions with or without further admixture with caustic or other components of heat-producing mixtures.

Example I Aluminum wire clippings 0.051 inch in diameter and averaging A inch in length were fed at room temperature and at a rate of 44 pounds per hour together with 0.51 gallon per hour of saturated sodium carbonate solution, saturated at 85 to 90 C., to a gas fired rotary drier (11 r.p.m.). The line gas temperature was about 360 C. Coated aluminum particles of excellent appearance, frosty white and uniformly coated were extracted from the drier at a temperature of 95 C.

Example II Bits of aluminum wire 0.051 inch in diameter by 34 inch in length were fed at 0.945 lb. per minute at room temperature into a gas-fired rotary drier together with a measured volume of soda ash solution saturated at 90 C. The solution was fed at the rate of 0.0123 gallon per pound of wire. Uniformly coated aluminum wire bits with a frosty white appearance were extracted at 85 C. an no operating difiiculties were encountered.

Example III Aluminum wire clippings inch in length and 0.060 inch in diameter were coated with soda ash by the procedure of Example I. A heat producing composition was prepared by mixing the ash-Dated aluminum particles with granular components in approximately the proportions indicated in the following table:

added without stirring to 150 ml. of water at about 70 F. in a 250 ml. graduate having a thermometer suspended with the bulb at the 10 ml. level, the following data were obtained:

Time, min.: Temp, C. 0.5 95

Example IV A hot, saturated solution of potassium carbonate was mixed with aluminum wire clippings 0.060 inch in diameter and averaging A; inch in length. The mixture was dried to produce aluminum particles having a gray coating.

Example V The procedure of Example IV substituting for the potassium carbonate, a mixture of 20% by weight of trisoduim phosphate and of dissodium hydrogen phosphate gave essentially similar results.

What is claimed is:

1. Process for coating aluminum particles with alkaline alkali metal salts to form discrete aluminum particles having thereon an adherent coating of said salts by the steps of mixing said aluminum particles with an aqueous solution of said salts in the proportion of from 1 to 10 pounds of said salts per 100 pounds of aluminum particles, drying the resulting mixture with agitation at temperatures of 50 to 150 C. and recovering the resulting discrete salt-coated aluminum particles.

2. Process according to claim 1 in which said aluminum particles have a maximum transverse dimension of 0.25 inch.

3. Process according to claim 1 in which said aqueous solution is an aqueous solution of soda ash and said proportion is from 2 to 6 pounds of soda ash per 100 pounds of aluminum particles 4. Process according to claim 3 in which said aqueous solution contains a minimum of 20 percent of soda ash.

5. Process according to claim 1 in which said aluminum particles are cut wire having a diameter of 0.01 to 0.15 inch and a length of 0.05 to 0.25 inch, said aqueous solution of soda ash contains 45 to 50 grams of soda ash per 100 grams of water, the proportion of soda ash to aluminum is from 4 to 5 pounds of soda ash per 100 pounds of aluminum and the drying temperature is between and 110 C.

6. Discrete aluminum particles having a uniform, adherent coating of alkaline alkali metal salt, said coating amounting to 1 to 10 pounds per pounds of aluminum.

7. Discrete aluminum particles having a uniform, adherent coating of soda ash, said coating amounting to 2 to 6 pounds per 100 pounds of aluminum.

8. A heat-producing composition consisting essentially of- Component: Percent by weight Caustic soda 40 to 67 Sodium chloride 0 to 25 Sodium nitrate 20 to 40 Sodium chlorite 0 to 10 Aluminum 2 to 8 Total 100 said aluminum being in the form of discrete particles having a uniform adherent coating of alkaline alkali metal salt, said coating amounting to 1 to 10 pounds per 100 pounds of aluminum.

9. A composition according to claim 8 in which said coating is soda ash and amounts to 2 to 6 pounds per 100 pounds of aluminum.

References Cited UNITED STATES PATENTS McNabb et al. 44-3 X McCulloch 117-128 Grant 44-3 Blackmun et a1. 252-103 X MacMahon 252-157 Walton et a1. 44-3 Standish et al 252-70 5 DANIEL E. WYMAN, Primary Examiner.

C. F. DEES, Assistant Examiner. 

8. A HEAT-PRODUCING COMPOSITION CONSISTING ESSENTIALLY OF- 